At 6-months probably rat pups, but it is best to confirm his/her weight on arrival & use the table above.
If you need a scale, I got this one on Amazon for only $11, it works great, accurate + simple to use:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
Sorry I'm not a tubber either...
BTW, I ordered rat pups from Big Cheese last week still in stock. I got 25 since I may need to move up after that & they will easily last 6-months in freeze (store in freezer bags and remove as much air as possible, vacuum sealer a plus)